The man in the grey overcoat is murdering single men across France.  The killings appear random, and yet… he shakes hands with each victim before putting a bullet through his heart.  The only witness is placed for his own safety inside the ultimate locked room: a concrete windowless bunker with walls one metre thick and covered by two metres of earth, with interior bolts and sentries on guard outside. The next morning, stupefied witnesses melt down the steel doors and bolts to find him dead.  One of the wildest and most imaginative serial killer/impossible stories ever written.